Elbow formed by cutting and method for manufacturing same

Abstract

A hole is formed in an elbow through the steps of: forming a starting hole in a material, the starting hole having an undercut remaining on a hole surface; finishing an inner diameter of the starting hole ( 11 -3 ) on one end side by revolving a side cutter (II) including an arc-shaped cutting edge and having an outer diameter smaller than a finishing hole diameter while rotating the side cutter (II) in such a posture that the side cutter (II) is inclined in a predetermined direction relative to the material ( 12 ), the revolving being carried out so that the side cutter moves along a hole surface to be finished; and finishing the inner diameter of the starting hole ( 11 -3 ) on another end side by revolving the side cutter (II) while rotating the side cutter (II).

1 . A method of manufacturing an elbow having a center axis that is bent smoothly at a predetermined curvature, the method comprising:
 preparing a metal material having a through hole; and   finishing an inner surface of the through hole using a cutter, having cutting edges around an axis of the cutter and having an outer diameter smaller than a diameter of the through hole, by rotating the cutter to form the inner surface while the cutter is inclined at a constant angle with respect to the metal material and revolving along a helical trajectory, such that any cross-section of the through hole that is parallel to an end surface of the cutter and perpendicular to the center axis of the elbow is cut into a circle, whereas any cross-section of the through hole that is parallel to the end surface of the cutter and not perpendicular to the center axis of the elbow is cut into an oval.   
     
     
         2 . The method of  claim 1 , further comprising machining the metal material such that a tube wall thickness on an outer side of a bend in the elbow is larger than a tube wall thickness on an inner side of the bend in the elbow, wherein the through hole is formed such that a center axis of the through hole is eccentrically located with respect to a center axis of an outer surface of the elbow. 
     
     
         3 . The method of  claim 2 , wherein the through hole is formed and finished such that the outer side of the bend is located at a position separated by 180° from a position of the inner side of the bend. 
     
     
         4 . The method of  claim 2 , wherein the through hole is formed and finished such that a wall thickness of the elbow gradually increases from the inner side of the bend to the outer side of the bend. 
     
     
         5 . The method of  claim 2 , wherein the through hole is formed and finished such that the tube wall thickness on the outer side of the bend is larger than the tube wall thickness on the inner side of the bend. 
     
     
         6 . The method of  claim 1 , wherein the through hole is formed and finished such that the through hole has a center axis that is bent smoothly at a predetermined curvature, without any machining remainder part inside and having a cross section, orthogonal to the center axis, that is a true circle, and wherein the method further comprises machining the metal material to comprise a straight part on at least one end side of the elbow. 
     
     
         7 . The method of  claim 1 , further comprising machining the metal material to comprise integral flanges at both end portions of the elbow. 
     
     
         8 . A method of manufacturing an elbow having a center axis that is bent smoothly at a predetermined curvature, the method comprising:
 preparing a metal material having a through hole; and   finishing an inner surface of the through hole using a cutter, having cutting edges around an axis of the cutter and having an outer diameter smaller than a diameter of the through hole, by rotating the cutter to form the inner surface while the cutter is inclined at a constant angle with respect to the metal material and revolving along a helical trajectory, such that each cross-section of the through hole that is parallel to an end surface of the cutter and not perpendicular to the center axis of the elbow is cut into an oval, and such oval cross sections include a first oval cross-section and a second oval cross-section, and the first oval cross-section of the through hole is different in size and shape from the second oval cross-sections of the through hole.   
     
     
         9 . A method of manufacture comprising:
 preparing a metal material having a through hole; and   finishing an inner surface of the through hole using a cutter, having cutting edges around an axis of the cutter and having an outer diameter smaller than a diameter of the through hole, by rotating the cutter to form the inner surface while the cutter is inclined at a constant angle with respect to the metal material and revolving along a helical trajectory, such that any cross-section of the through hole that is parallel to an end surface of the cutter and perpendicular to a center axis of the through hole is cut into a circle, whereas any cross-section of the through hole that is parallel to the end surface of the cutter and not perpendicular to the center axis of the through hole is cut into an oval.